1. Field of the Invention
This invention relates to microfluidic systems, apparatus, and methods for handling or processing fluid suspensions of dielectric particles including living cells, spores, viruses, polymer beads, and aggregates of macromolecules. In particular, the invention involves the use of dielectrophoresis (DEP) induced forces to manipulate or control the velocity, including direction, of dielectric particles in microfluidic devices.
2. Description of Related Art
U.S. Ser. No. 11/167,428 discloses arrangements of electrodes used to engineer microfluidic devices that achieve programmable, high efficiency particle separations. The particles are separated in a separation chamber comprising at least one pair, or preferably two opposing pairs, of electrodes that generate c-DEP forces, which act on a mixture of particles in a suspending medium. Particles are deflected and/or blocked by DEP forces generated by the electrodes. Particles deflected by the two pairs of electrodes can be shunted into a side channel for further concentration and analysis. Alternatively, particles blocked by two pairs of electrodes can be released by changing the applied c-DEP forces. The separation chamber can be tuned to trap/separate different types of particles by altering the voltages, AC frequencies, and/or the spacing between electrode pairs.
A feature that distinguishes the invention disclosed in U.S. Ser. No. 11/167,428 from other DEP separation techniques using coupled electrode pairs is the electrode configuration of the electrically coupled electrode pair. Applying an electric potential to an electrically coupled pair of electrodes adjacent to one another on the same surface results in a electric and DEP fields that are completely different from the fields generated when a potential is applied to a pair of electrodes located opposite one another. FIG. 1 shows the electric field lines FL and isopotential contours IC generated by electrodes conventionally located on opposing surfaces (FIG. 1A) and those generated by adjacent, electrically coupled electrodes located on the same surface (FIG. 1B) as in the used in the present invention. FIG. 1B shows two pairs of electrodes so that the advantages of two pairs of electrodes located opposite one another can be explained but the use of two pairs of electrodes, while preferred, is not required.
Methods and devices using an electrically coupled electrode pair 33, 34 arranged in opposition (FIG. 1A) generate a pattern of electric field lines FL that traverse the flow channel between them. Methods and devices using adjacent, electrically coupled electrodes pairs 3,4 and 13,14 separated by a gap distance arranged (FIG. 1B) generates field lines FL that originate and terminate on the same side of the flow channel. The electric field and isopotential geometries shown in FIG. 1B cannot be produced by any combination of electrode pairs that are electrically coupled and on opposite sides of the flow channel. The isopotential contours IC and potential gradients generated by the two electrode arrangements also differ. The magnitude of the potential gradients are proportional to the spacing between isopotential lines in FIG. 1. A particle moving from left to right in the flow channel experiences a much higher and more symmetrical potential gradient when the electrodes are arranged as in FIG. 1B than it does when the electrodes are arranged as in A. The higher, more symmetric potential gradient resulting from consecutive, electrically coupled electrodes that are adjacent to one another and separated by a gap distance as shown in FIG. 1B provides more effective separation than the potential gradient shown in FIG. 1A. The electric field strengths in both cases can be increased by moving the coupled electrodes closer together while applying the same constant or by increasing the applied potential. Moving the coupled electrodes closer together requires reducing the flow channel dimensions for oppositely arranged electrodes as in FIG. 1A but not for pairs of adjacent electrodes as in FIG. 1B. Consequently, devices with the electrode configuration shown in FIG. 1B can operate at lower applied potentials while maintaining higher flow volumes and flow rates than devices with the electrode configuration shown in FIG. 1A. The use of lower applied voltages reduces the risk of damaging cells, viruses, and other biological particles being separated.
The DEP force produced by the electrode configuration in FIG. 1B can be adjusted by altering the electrode gap distance, the electrode geometry, channel geometry, the potential and/or frequency and/or waveform of the applied potential. The flow rate determines the hydrodynamic force acting on the particles, which is strong enough for non-selected particles to overcome the lateral DEP force at each set of electrodes while selected particles are halted or diverted into one or more side channels.
The invention disclosed in U.S. Ser. No. 11/167,428 discloses a separation chamber comprising a flow channel comprising a single pair of consecutive, electrically coupled, planar electrodes at the bottom surface of a flow channel or two pairs of consecutive, electrically coupled, planar electrodes are placed on opposite surfaces of a flow channel. The DEP force generated by a single pair of electrodes levitates selected particles and can be used to prevent selected particles from traversing the electrodes to divert them into a side channel or to prevent them from leaving the flow channel. The lateral component of the DEP force can be used to enhance the motion of particles into a side channel. The magnitudes of the levitating and lateral forces used to capture and/or divert particles decrease as distance from the coupled electrode pair increases. An additional pair of consecutive, electrically coupled planar electrodes can be placed on an opposite side of a flow channel from a first electrode pair. Opposing electrode pairs allow for higher flow volumes because the height of the flow channel can be increased while maintaining the same DEP forces without increasing the potential applied to the electrodes. Alternatively, the configuration of the opposing electrode pairs can be used to strengthen the DEP forces relative to the single electrode pair configuration.
The electrode configurations disclosed in U.S. Ser. No. 11/167,428, while an improvement over previous electrode configurations, do not provide for the separation of more than two populations of particles. Additionally, hydrodynamic flows in some circumstances can reduce the efficiency of separation and cause contamination of selected particles by non-selected particles.